System for reading an information strip containing optically coded information

ABSTRACT

A reading arrangement includes at least one linear detector arrangement which is arranged in parallel relationship above a reading plane and behind an optical imaging element and is oriented on to a reading region of the reading plane, lighting devices and an evaluation unit and serves for machine reading of an information strip with optically encoded information. The light which is scattered or diffracted out of the reading region in which the information strip to be read off by machine is disposed into the optical imaging element is so projected on to the photosensitive faces of the detector arrangement that an image of the reading region is formed. The detector arrangement produces two detector signals and from a comparison of the detector signals, the read information is determined and its authenticity verified.

BACKGROUND OF THE INVENTION

The invention relates to an arrangement for machine reading ofinformation strips with optically encoded information.

Such reading arrangements are used for the machine checking of documentssuch as identity cards, credit and payment cards, passes, banknotes,stocks and shares and securities, valuable articles or products and thepackaging thereof and so forth, which have an information strip withoptically encoded information.

EP 0 718 795 A1 discloses a reading arrangement for information stripswith optically encoded information. Optical markings are arranged on theinformation strip in bit lines, wherein at least two bit lines with anidentical division into surface portions of equal size are required.Each surface portion is occupied for example by an optical diffractionelement. The diffraction elements of the same bit line involve the samegrating parameters (spatial frequency, profile shape, azimuth etc) anddiffer from the diffraction elements of the adjacent bit line. Arespective surface portion from the one bit line forms, with theadjacent surface portion from another bit line, a bit pair representingan individual bit of the item of information. In the case of thoseinformation strips, after manufacture it is possible for an item ofinformation to be individually written once, wherein in the operation ofwriting the information in one of the two surface portions of the bitpair, the optical characteristics of the surface portion areirreversibly modified. A number of embodiments of the information stripsare described. Specific structures of the diffraction elements are knownfor example from WO 97/19821 and WO 98/10324.

It is also known (EP 0 883085 A1) for each surface portion of asingle-line information strip to be made up from a plurality of partialsurfaces which are occupied alternately by one of two different opticaldiffraction elements from the set a, b, c, d etc. The diffractionelements of one of the sets a, b, c, d etc involve the same gratingparameters (spatial frequency, profile shape, azimuth etc) and differfrom the diffraction elements of the other sets. Each surface portiondiffers from its two neighbours by virtue of the choice of thediffraction elements for the partial surfaces. The information of thoseinformation strips is the same in all and cannot be individuallymodified for each information strip.

A bar code which is made up from diffraction elements and a reader whichis suitable for labels with such a bar code is described in EP 0 366 858A1. The information content of that bar code cannot be individuallymodified.

The reading arrangements described in the quoted documents scan theinformation by means of a narrow light beam which is incident inperpendicular relationship on to the plane of the information carrierand observe the light which is diffracted at the diffraction elements ofthe information carrier, by means of photoelectric elements. Thosereading arrangements suffer from the disadvantage that the light beammust be moved relative to the information carrier for scanning theinformation on the information strip.

Without an additional and expensive scanning track on the informationcarrier, in accordance with EP 0 718 795 A1 the speed of that relativemovement must be uniform so that the information which is read off canbe recognised.

The reader described in WO 98/55963, instead of the usual discretephotoelectric elements, also uses photodetector arrays which are alsoknown by the name ‘Charge Coupled Device’ or CCD. An optical elementconverts the light emitted from a point source into a parallel lightbeam which is incident in perpendicular relationship on to the entireface with the optical-diffraction markings, the light beam illuminatingat least the entire face with the optical-diffraction markings. Thelight diffracted at those markings is collected again by the opticalelement and focused in point form on the photodetector arrays. Thereader manages without a relative movement between the incident lightand the information strip, and it is substantially independent of thedistance between the markings and the optical element. An embodiment canalso tolerate azimuth errors. A limitation in terms of the scope of theinformation has to be accepted as a disadvantage.

SUMMARY OF THE INVENTION

The object of the present invention is that of providing a simple andinexpensive arrangement for the machine reading of information stripswith optically encoded information, which detects the information with ahigh level of reliability.

In accordance with the invention the stated object is attained by thefeatures recited in the characterising portion of claim 1. A readingarrangement includes at least one linear detector arrangement which isdisposed parallel to a reading plane and behind an optical imagingelement and which is directed on to a reading region of the readingplane, lighting devices and an evaluation unit, and serves for themachine reading of an information strip with optically encodedinformation, which is in the reading region. The light which isdiffracted or scattered out of the reading region in which theinformation strip to be read off by machine is disposed into the opticalimaging element is projected on to the photosensitive faces of thedetector arrangement in such a way that an image of the reading regionis formed. The reading region is laterally inclinedly lit by arespective one of the lighting devices. In a first reading phase thedetector arrangement produces detector signals S(1) and in a secondreading phase the detector signals S(2), wherein lighting directions α,β, and/or the quality of the light used for lighting the reading regionare different in the reading phases. From a comparison of the detectorsignals S(1) and S(2), the information which is read off is determinedand its authenticity verified.

Advantageous configurations of the invention are set forth in theappendant claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in greater detail hereinafterand illustrated in the drawing in which:

FIG. 1a shows an arrangement for the reading operation, FIG. 1b is aview in section of the arrangement for the reading operation,

FIG. 2a shows an information strip,

FIG. 2b is a view in section of the information strip,

FIG. 3 shows a detector arrangement,

FIG. 4 shows a first and second sequence of detector signals, and

FIG. 5 shows a document.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1a, reference 1 denotes a document, reference 2 aninformation strip, reference 3 an optical imaging element, reference 4 adetector arrangement, reference 5 a first lighting device, reference 6 asecond lighting device, reference 7 a reading plane, references 8 and 9edge portions of the reading plane 7 and reference 10 an opening foreasier removal of the read document 1. The document 1 lies on thereading plane 7 and on its front side 11 has the information strip 2.The edge portions 8 and 9 of the reading plane 7 position the document 1in such a way that the information strip 2 comes to lie over its entirelength completely within a strip-shaped reading region 12. For reasonsof illustration in the drawing, the reading region 12 is bordered by abroken line. The reading region 12 is established by the imaging element3 and/or the detector arrangement 4, as the region of the reading plane7, the image of which is formed by the imaging element 3 onphotosensitive faces of the detector arrangement 4. The reading region12, the image of which is formed on the detector arrangement 4 by meansof the imaging element 3, is smaller at least in its longitudinaldirection than the photosensitive faces. A notional plane of symmetry 13is parallel to an optical axis of the imaging element 3 and intersectsthe imaging element 3, the detector arrangement 4 and the reading region12 centrally in the longitudinal direction. In an embodiment of thereading arrangement, the plane of symmetry 13 is perpendicular to thereading plane 7, while in another embodiment it is inclined. Thedocument 1 is laid with the information strip 2 directed towards theimaging element 3 on the reading plane 7 and is so oriented by means ofthe edge portions 8, 9 that the information strip 2 is in the readingregion 12. The spacing H between the photosensitive faces of thedetector arrangement 4 and the reading region 12 is the spacing betweenthe image and object planes of the imaging element 3.

The reading arrangement includes at least the optical imaging element 3,the detector arrangement 4, at least one lighting device 5, 6 and thereading plane 7. To make description easier herein, a right-angledcoordinate system which is oriented on to the reading region 12 is used,in parallel relationship with the reading plane 7. The ordinate Y of thecoordinate system is oriented parallel to the shorter side of thereading region 12 while the abscissa X is oriented parallel to thelongitudinal side of the reading region 12.

A suitable form of imaging element 3 is an individual lens which is veryexpensive because of the size required, a field or panel with aplurality of small lenses of a diameter in the range of between 0.01 mmand 2 mm, or small cylindrical lenses with their axis parallel to theordinate Y, or Fresnel lenses with the properties of the round lenses orthe cylindrical lenses, wherein the field or panel involves at least thedimensions of the reading region 12. A bundle of optical waveguides canalso be used as the imaging element 3, in particular such bundles withimaging properties such as for example the SELFOC® ‘lens arrays’ fromNippon Sheet Glass Co Ltd, Tokyo, Japan, are highly suitable.

The information strip 2 can be integrated directly into the document 1,for example in the case of documents 1 in card form, coins, tokens etcor can also be stuck in the form of a label on to the kinds of document1 referred to in the opening part of this specification. The informationstrip 2 is rectangular and has on at least two lines a division intoequal-sized raster or grid elements 14, 15. The longitudinal boundary ofthe information strip 2 is disposed parallel to the abscissa axis X. Thegrid elements 14 of the first line all have the same region of theordinate Y₁ and the grid elements 15 of the second line all have thesame region of the ordinate Y₂. The N grid elements 14 and 15respectively in each line differ in the abscissa X_(k), wherein theindex k ranges through the values of between 1 and N. In the new state,that is to say in the unwritten state, of the information strip 2, the Ngrid elements 14 exhibit an identical optical behaviour. The opticalbehaviour of the N grid elements 15 is also identical and differs fromthe optical behaviour of the grid elements 14.

Referring to FIG. 1b, shown therein is a view in section of the readingarrangement, with the reading plane 7 and the plane of symmetry 13 beingperpendicular to the plane of the section. The reading arrangement isdisposed in a housing 16 which keeps out external light and preventslight from the lighting device 5, 6 from penetrating directly to thedetector arrangement 4. Two lighting devices 5, 6 extend along theoptical imaging element 3 above the document 1 parallel to the plane ofsymmetry 13 and to the reading plane 7. The imaging element 3 is spacedfrom the surface 11 (FIG. 1a) in such a way that each lighting device 5or 6 respectively is solely capable of completely and as uniformly aspossible illuminating the reading region. As shown in the drawing, thelight paths can extend rectilinearly and/or can be deflected by means ofprisms, mirrors, optical waveguides and so forth, for example in orderto afford a reading arrangement which is suitably adapted to theinstallation conditions involved.

The optical imaging element 3 collects the light 7 which is incident atthe information strip 2 at its acceptance angle and which ideally isdeflected substantially almost parallel to the plane of symmetry 13 byscatter or diffraction, in such a way that at least in its longitudinalextent an image of the information strip 2 is formed on thephotosensitive faces of the detector arrangement 4. Light 18 reflectedat the surface 11 or other faces is not captured by the imaging element3.

In the simplest case the lighting devices 5, 6 involve a linear extentof a light source in parallel relationship to the longitudinal side ofthe reading region 12. Examples are double-ended tubular incandescentlamps with an extended incandescent wire, fluorescent tubes or a lineararrangement of light emitting diodes and so forth. Arranged between thelighting devices 5 and 6 and the reading region 12 there isadvantageously an optical system 19 which produces a lighting beam 20and 21 respectively. The optical system 19 homogenises the intensity ofthe lighting effect in the reading region 12 and/or collimates thelighting beam 20 and 21 respectively. The light of a point-form lightsource, for example produced with a laser diode, is also expanded by theoptical system 19 to the dimensions of the reading region 12. Thatprovides for a uniform lighting effect in the entire reading region 12.The lighting directions α, β are the projections of the lighting beams20, 21 which are incident on the reading region 12, on to a plane whichis perpendicular both to the plane of symmetry 13 and also to thereading plane 7, and are incident on the reading region 12 at lightingdirections α, β. The lighting direction α and β respectively forms withthe reading plane 7 an angle which is in the range of between 10° and60° for the lighting direction α and in the range of between 120° and170° for the lighting direction β. The optical system 19 comprises adiffuser lens or screen, a cylindrical lens, a holographically generatedoptical element (HOE) and so forth, individually or in combination witha color filter and/or with a polarisation filter and so forth. Thequality of the light in the lighting beam 20 and 21 respectively can beestablished with the filters. For each line of the information strip,which is to be successively read out, the lighting is established in thereading region 12 in terms of the quality of the light and/or thelighting direction α, β. The reading arrangement produces successivelyin accordance with the number of lines in the information strip 2 two ormore lighting beams 20, 21. The lighting devices 6 can be arranged onthe same side of the imaging element 3 in order to illuminate thereading region 12 from the various lighting directions α, β and/or withthe different qualities of light. An embodiment with a lighting device 5in which the quality of the light in the lighting beam 20 is variable orat least two qualities of light, for example polychromatic light, aresimultaneously emitted, is to be interpreted as a special case. Inanother embodiment the lighting devices 5, 6 are arranged on both sidesof the plane of symmetry 13, symmetrically or asymmetrically.

If the entire photosensitive face of the detector arrangement 4 is inthe shape of a rectangle, an additional optical element, aone-dimensional diffuser 23, is advantageously arranged between theimaging element 3 and the detector arrangement 4, in order to increasethe positional tolerance of the information strip 2 in the readingregion 12 and to lower the sensitivity to local defects in the gridelements 14, 15. The one-dimensional diffuser 23 blurs the imagingeffect of the grid elements 14, 15 in the direction of the ordinate Y insuch a way that at least a part of the deflected or diffracted light 17of both grid elements 14 and 15 extends over the entire width of thetotal photosensitive face of the detector arrangement 4. An anisotropicmatt structure, a simple diffraction grating with a spatial frequency ofless than 150 lines/mm or cylindrical lenses have that property ofdiffusing light only parallel to one plane. In order to recognise thedifferences produced by the information strip 2 in polarisation of thelight, a polarisation filter is arranged as an analyser 22 between theimaging element 3 and the detector arrangement 4. The relief structureof the one-dimensional diffuser 23 can be impressed directly into theplastic foil or sheet of the analyser 22 (type Polaroid®) so that theanalyser 22 and the one-dimensional diffuser 23 form a single component.

The reading arrangement has an evaluation unit 24 which controls thereading cycle and which is adapted to recognise the item of information.For that purpose, the evaluation unit 24 is connected to the lightingdevices 5 and 6 by way of control lines 25, 26 so that the lightingdevices 5 and 6 can be sequentially switched on and off by theevaluation unit 24. The lighting direction α and β respectively and thequality of the light in the lighting beam 20 and 21 respectively isestablished for illumination of the reading region 12 by virtue ofswitching on the lighting device 5 or 6 respectively. The detectorarrangement 4 is connected to the evaluation unit 24 by way of signallines 27. By way of the one signal line 27 the evaluation unit 24 sendsa reading signal to the detector arrangement 4 and causes read-out ofdetector signals S(1) and S(2) which correspond to the brightnessvalues, recorded by the photodetectors 28, of the information strip 2whose image is formed on the photosensitive faces of the detectorarrangement 4. The detector signals S(1) and S(2) go by way of the othersignal lines 27 into one of the two data stores 29, 30 of the evaluationunit 24.

In an embodiment, the reading plane 7 is not connected to the rest ofthe reading arrangement. In this embodiment, the reading arrangement hasa window for delimiting the reading region 12. The frame 31 of thewindow, which is part of the housing 16, serves as a support for thedocument 1, wherein the surface 11 (FIG. 1a) of the document 1 isdirected with the information strip 2 for the reading operation towardsthe window. In an embodiment without the frame 31 the reading plane 7 isspaced from the housing 16. The document 1 can be easily oriented byhand in the lit reading region 12 until the reading arrangementmechanically reads off the information correctly from the informationstrip 2. A monitor 32 which is connected to the evaluation unit 24 byway of a line 33 makes it possible to recognise successful reading ofthe information strip 2. In the simplest case the monitor 32 is ared/green signal which changes from red to green when the information iscorrectly recognised. The line 33 can also pass the read-out informationto other units (not shown here) which for example release a block, sendthe read-out information to a central station, and possibly interrogateadditional data associated with the read-out information, from thecentral station, and so forth.

The reading cycle advantageously comprises two reading phases forreading the information out of the information strip. Each two readingphases are separated by a respective reading break in which the detectedinformation is processed by the evaluation unit 24. By way of switchingthe lighting device 5 or 6 respectively on and off, the evaluation unit24 controls the lighting direction α, β and/or the quality of the lightemitted in the lighting beam 20 and 21 respectively. Each reading phasediffers from the preceding one by the lighting direction α, β and/or thequality of the emitted light. At the beginning of the reading phase, thelighting device 5 or 6 is switched on and the reading region 12 is litup. At the end of the reading phase the evaluation unit 24 implementsthe reading-out operation and causes transmission of the brightnessvalues recorded by a plurality of photodetectors 28 by way of the signalline 27 and switches the lighting device 5 or 6 off. The evaluationdevice 24 receives a first sequence of signals whose signal valuesreproduce the brightness distribution on the photosensitive faces of thedetector arrangement 4 during the first reading phase in which thereading region 12 is lit from the first lighting direction α and/or withthe first quality of the emitted light and light 17 reflected into theimaging element 3 originates from the grid elements 14 (FIG. 1a) of thefirst line, which are not altered in terms of their optical behaviour.In the subsequent second reading phase the evaluation unit 24 receives asecond sequence of signals whose signal values correspond to thebrightness distribution during the lighting of the reading region 12from a second lighting direction β and/or with a second quality of theemitted light and the reflected light 17 originates from the gridelements 15 (FIG. 1a) of the second line, which are not altered in termsof the optical behaviour involved.

The reading arrangement is to be adapted to the technology of theinformation strip 2. In a simple embodiment, the information strip 2 isa colored, diffusely scattering substrate, for example paper, plasticmaterial, metal and so forth, while the grid elements 14 and 15 are ofcomplementary colors (for example red-green). By virtue of being printedon in a color which absorbs the colors red and green (for exampleblack), the grid elements 14 and 15 can be altered in terms of theiroptical behaviour. In accordance with the reading phase the lightingdevice 5 or 6 is switched on, which at a lighting angle α or βrespectively lights the reading region 12 with red or green light insuch a way that the light which is diffusely scattered in the readingregion 12 and received by the imaging element 3 forms an image of thered or green grid elements 14 and 15 respectively with a high brightnessvalue on the photosensitive faces of the detector arrangement 4. Incontrast thereto the brightness value of the captured scatter light fromthe grid elements 14, 15 which are printed black or from the green gridelements 15 in red light or the red grid elements 14 in green light isslight compared to the high brightness values.

FIG. 2a shows an example of a two-line information strip 2 with N gridor raster pairs. The k-th grid pair is formed from a grid element 14 ofthe first line and a grid element 15 of the second line, with the samevalue for the abscissa X_(k). Each grid pair affords space for a bit ofan item of digital information, wherein in the operation of writing tothe information strip 2 the optical behaviour of one of the two gridelements 14 and 15 respectively is modified, which for technical reasonsis illustrated in the drawing of FIGS. 1a and 2 a by hatching of thesurface of the grid element 14 and 15 respectively. As only two out offour possible states of the grid pair are used, an item of written-ininformation cannot be altered. If both grid elements 14 and 15 aremodified in terms of their optical behaviour, that indicatesmanipulation or excessive use of the document 1 (Figure. a). Aninformation strip 2 which is not written is distinguished by unmodifiedgrid elements 14 and 15 in the same grid pair, as for example the gridpairs N−10 through N.

The k-th grid pair whose grid element 15 in the second line is modifiedrepresents for example the bit value ‘1’ and the k+1-th grid pair whosegrid element 14 in the first line is modified represents the bit value‘0’. The first line of the information strip 2 therefore has the sameinformation as the second line, but in the second line the sequence ofthe grid elements 15 which are modified and unmodified in respect ofoptical behaviour is interchanged or inverted in relation to thesequence of the modified and unmodified grid elements 14 in the firstline. If the two lines are read in succession, that inversion of thesuccession involved can be easily checked by machine. In the firstreading phase the first line is read from the first grid pair; the firstsequence begins with ‘ummumuumuuummumuu’, while in the second readingphase, the second line, read in the same direction, the beginning of thesecond sequence reads ‘muumummummmuumumm . . . ’, in which ‘m’ standsfor a modified grid element 14 or 15 and ‘u’ stands for an unmodifiedelement. By inversion of the second sequence (interchange of m and u)and comparison with the first sequence, the read-out information ischecked for correct reading-off and authenticity. The resulting sequence‘10010110111001011 . . . ’ is the recognised information, having regardto the association of the bit values.

The sequence of information in an example is arranged between apredetermined start sequence and stop sequence each for example of 8bits. The start sequence indicates to the reading arrangement that asubsequent item of information of predetermined length is being read inthe same succession, in relation to the stop sequence. If the stopsequence is read first, it signals to the evaluation unit 24, reading ofthe subsequent item of information in the reversed succession. The itemof information can also be arranged in the form of a palindrome, inwhich case the first half contains all the information which is repeatedin the second half in the reverse succession of the bits. In anotherembodiment, the start and stop sequence is fixedly predetermined inmanufacture of the information strip 2 and does not need to be producedwhen writing in the information.

A higher level of information density and a better signal-to-backgroundratio is enjoyed by the information strips 2 whose grid elements 14, 15have fine relief structures which reflectingly diffract light incidentfrom a predetermined direction in the reading region with a high levelof intensity into the direction which is predetermined by the imagingelement 3. The grating lines of the fine relief structures areadvantageously oriented substantially parallel to the abscissa axis X.The high level of intensity of the light 17 (FIG. 1b) diffracted at thegrid elements 14, 15 makes it possible to use smaller grid elements 14,15 for the information strip 2, without having to accept losses in termsof reading reliability. Typically, a grid pair measures between 0.5 and3 mm in width and between 0.1 and 0.5 mm in length.

The reading arrangement in FIG. 1b is designed for reading theinformation strips 2 of a width of 1.5 mm and a total length of 25 mmwith a capacity of 160 bits for the item of information and in addition8 bits for each of the start and stop signals, and can be implementedvery compactly in a small space. It is composed at least of thefollowing components:

a) The detector arrangement 4 is a component which is available underthe designation ILX511 2048-pixel CCD Linear Image Sensor from SONY. Thenumber of photodetectors 28 is M=2048. They each have a photosensitiveface measuring 14 μm×200 μm, while the linear distribution along theabscissa axis X (FIG. 3) is 14 μm and the total length is 28.7 mm;

b) the imaging element 3 is the SELFOC® ‘Lens Array’ SLA-20B, a dual-rowbundle of 6.7 mm long, thick lenses of between 0.8 and 1.2 mm indiameter, in which the spacing H between the object plane and the imageplane is about 15.4 mm and imaging is in the ratio of 1:1;

c) the lighting devices 5, 6 are arranged symmetrically with respect tothe plane of symmetry 13 and are formed by means of a linear row oflight emitting diodes. Their color light and lighting beam 20, 21 arematched to the grid elements 14, 15. In order to homogenise the lightfrom the point-form light emitting diodes in the reading plane 12, theoptical system 19 has uniformly scattering, properties;

d) the one-dimensional diffuser 23 and optionally the analyser 22; and

e) the evaluation device 24 with monitor 32.

The length of each grid pair k (FIG. 2a), as measured: on the abscissaaxis X, is thus 0.14 mm which is scanned by in each case approximately10 photodetectors 28 arranged in a line in mutually juxtaposedrelationship. The reading arrangement can be disposed in a housing 16involving the approximate dimensions of 30×40×20 mm; that facilitatesinstallation in other items of equipment (not shown), for examplereading apparatuses for IC-cards etc. The advantage is the compactinexpensive structure of the reading arrangement. Reading-out andrecognition of the item of information are effected within a fewmilliseconds so that the information strip 2 can be read off even from amoving document 1. The movement is advantageously in the direction ofthe ordinate Y (FIG. 1a), that is to say transversely with respect tothe information strip 2.

FIG. 2b shows the information strip 2 in an embodiment with reliefstructures, as a view in cross-section. The information strip 2 is alaminate comprising plastic layers 34, 35, 36, 37. At least the coverlayer 34 and the embossing or stamping layer 35 are transparent inrelation to the light of the lighting so that the information can beread out through those two layers 34, 35. The detailed structure of thelaminate is described for example in EP 0 401 466 B1. The cover layer 34has at least a high level of scratch resistance, as is known fromlacquers, in particular lacquers which are hardened by UV, or forexample PC, PETF or other foils, even in thicknesses in the micrometerrange. The stamping layer 35 and the protective layer 36 include attheir joint interface fine relief structures in the form of diffractionstructures 38, 39. A sudden change in the refractive index at theinterface increases the intensity of the diffraction effects at thediffraction structures 38, 39. That is effected by an additional layer,which is between 10 and 500 nm in thickness, of metal, semiconductor ora dielectric in the interface, or solely by using materials for thestamping layer 35 and the protective layer 36, which involve adifference in refractive index. The adhesive layer 37 joins the laminateto the document 1. Both cold adhesives and also hot melt adhesives haveproven their worth here. The adhesive layer 37 is unnecessary if thematerial of the protective layer 36 itself is an adhesive. The materialof the information strip 2 is produced in the form of a strip, fromwhich suitable pieces are cut off and joined to the document 1. If thecover layer 3 and the stamping layer 35 are made from the same material,it is not possible to see any boundary between the cover layer 34 andthe stamping layer 35. For example, the information strip 2 can beinconspicuously embedded within a hologram image or in a mosaic of otherdiffraction elements, the grating parameters of which differ from thoseof the two diffraction structures 38 and 39 in such a way that the otherdiffraction elements do not deflect light from the lighting devices 5, 6into the imaging element 3.

In the unwritten condition of the information strip 2 all grid elements14 have the same diffraction structure 38 and the grid elements 15 havethe same diffraction structure 39. The diffraction structures 38 and 39must differ at least in respect of one parameter of the gratingstructure such as spatial frequency, azimuth, grating profile and soforth. The diffraction structure 38 or 39 respectively satisfies therequirement of diffracting the lighting beam 20 or 21 into the imagingelement 3 and diffracting the other lighting beam 21 and 22 respectivelyin such a way that no or distinguishably less light of the lighting beam21 and 20 respectively passes into the imaging element 3. The unwritteninformation strip 2 has no information as all diffraction structures 38,39 are optically active. When the information is written in, thediffraction structures 38, 39 which are no longer required areirreversibly modified in respect of their optical behaviour so that atbest scatter light of low intensity passes into the imaging element 3from the diffraction structures 38, 39 which are not required. Methodsand means for irreversibly modifying the optical behaviour of thediffraction structures 38, 39 are described in above-mentioned EP 0 718795 A1, column 4, line 33 to the top of column 6.

In an embodiment of the information strip 2, the grid pairs of the startand stop sequences are already fixedly encoded upon manufacture, inwhich case, instead of the diffraction structures 38 and 39 which aremodified in terms of optical behaviour in the grid element 14 or 15respectively there is a mirror or a third relief structure. The thirdrelief structure does not diffract the lighting beams 20, 21 into theimaging element 3 (FIG. 1b) or diffusely scatters same, as a mattstructure. In a further embodiment of the information strip 2 all gridelements 14, 15 and thus all the information are fixedly encoded in thesame way as the start and stop sequences. The grid elements 14, 15 of anembodiment of the information strip 2 with fixedly encoded informationcan also merely consist of one line, in which case, arranged in thatline, instead of the first diffraction structures 38 which are notrequired for the information, are the second diffraction structures 39.The information strip 2 of this embodiment can be read out with the samereading arrangement.

In another embodiment of the information strip 2 the diffractionstructures 38, 39 are incorporated directly into the base material ofthe document comprising laminate, plastic, metal and so forth. The basematerial is formed from the layers 34, 35. The reading-out operation iseffected through the transparent protective layer 36.

In the illustrated example the asymmetric diffraction structures 38 and39 differ only in respect of azimuth, the difference being 180°, that isto say they are arranged in mirror image symmetry. The two lightingdevices 5 and 6 are arranged symmetrically with respect to the plane ofsymmetry 13 (FIG. 1a) and are adapted to produce monochromatic light.When the information strip 2 is disposed in the reading region 12 (FIG.1a) which in the first reading phase is illuminated with light of thefirst lighting beam 20 from the first lighting direction a, the imagingelement 3 (FIG. 1a) only collects the light 17 (FIG. 1b) which isreflected and diffracted at the diffraction structure 38 of theunmodified grid elements 14, 15, and forms the image of the brightnessdistribution on the photosensitive faces of the detector arrangement 4(FIG. 1a). In the first and second reading phases respectively, at thefirst and second diffraction structures 38 and 39, the first and secondlighting beams 20 and 21 respectively are diffracted with a high levelof efficiency into the plus first order and at the same time diffractedinto the minus first order with a markedly lower level of efficiency atthe second and first diffraction structures 39 and 38 respectively. Theimaging element 3 collects the diffracted reflected light 17 (FIG. 1b)and produces brightness values which are to be markedly distinguished onthe photosensitive faces of the detector arrangement 4. Any scatterlight which is detected by the imaging element 3 has only slightdifferences in intensity in the two reading phases and does not disturbthe brightness distribution on the photosensitive faces of the detectorarrangement 4. If the asymmetrical diffraction structures 38 and 39additionally differ in their spatial frequencies, they can be selectedin such a way that the first and second lighting beams 20 and 21respectively, of the minus first order, which are diffracted at thesecond and first diffraction structures 39 and 38 respectively, are notdetected by the imaging element 3.

If the diffraction structures 38 and 39 differ only in respect ofspatial frequency, the lighting devices α, β and/or the wavelengths λ₁,λ₂ of the lighting beam 20, 21 must be adapted. The wavelengths λ₁, λ₂and the lighting directions α, β establish the spatial frequency for thediffraction structures 38 and 39.

Diffraction structures 38, 39 which are known from WO 97/19821, with lowspatial frequencies (between 50 and 250 lines/mm) and with a gratingprofile involving a height of between 0.7 μm and 1.5 μm, exhibit anachromatic diffraction behaviour, that is to say even a polychromaticlight can be used for lighting the reading region 12 if such diffractionstructures 38, 39 deflect the tightly focused, polychromaticallydiffracted light into the imaging element 3.

WO 98/10324 describes diffraction gratings which differ only in terms oftheir polarisation capability. If such diffraction gratings are adoptedfor the diffraction structures 38, 39, lighting of the reading plane 12(FIG. 1a) is effected with differently polarised light, using apolarisation filter in the optical system 19 (FIG. 1b) for the lightingbeams 20, 21. In another embodiment the polarisation filter is arrangedas an analyser 22 between the imaging element 3 and the detectorarrangement 4 and lighting of the reading region 12 (FIG. 1a) iseffected with unpolarised light.

If the diffraction structures 38, 39 are symmetrical the lightingdevices 5, 6 can also be arranged on the same side of the plane ofsymmetry 13. If the lighting of the reading region 12 differs only inrespect of the wavelength of the light incident in the reading region 12(FIG. 1a) at the lighting direction ax, then a linear arrangement oflight emitting diodes is advantageously adopted, in which case the lightemitting diodes differ in the color of the emitted light. The lightemitting diodes of the various colors alternate in the lineararrangement in such a way that the reading region 12 is uniformlyilluminated in one color when only the light emitting diodes of the samecolor are simultaneously switched on in a reading phase. Light emittingdiodes which emit light in two or more colors are also suitable for thelinear arrangement, in which case the color is adjustable under externalactuation. Simultaneous actuation of the colors produces a polychromaticlight.

FIG. 3 shows the photosensitive side of the detector arrangement 4 withan image 40 of the grid pairs of the information strip 2 (FIG. 2a), theimage 40 being shown in broken line here for reasons of drawing andbeing produced by the imaging element 3 (FIG. 1b) without theone-dimensional diffuser 23 (FIG. 1b). In the first reading phase thereading region 12 (FIG. 1a) is lit with the lighting device 5 (FIG. 1a).In the image 40 the grid elements 14 of the first line, with theordinate Y=Z₁, which are shown with inclined hatching in the drawing andwhich are unmodified in terms of optical behaviour, are zones involvinga high level of light intensity. The grid elements 15 of the first line,which are shown without hatching and which are modified in terms ofoptical behaviour, and all grid elements 15 of the second line, with theordinate Y=Z₂, project light 17 (FIG. 1b) at at least 50% less intensityon to the detector arrangement 4 and are imaged in the form of darkzones. The lighting device 6 (FIG. 1a) is switched on in the secondreading phase so that only the image of the hatched grid elements 15 ofthe second line, which are unmodified in terms of optical behaviour, isformed in the image 40.

The commercially available, single-line detector arrangements 4 are of avalue of between 7 μm and 200 μm, for the width B. The subdivision alongthe abscissa axis X has a pitch of 7 μm, 14 μm or more, so that eachphotodetector 28 therefore has a photosensitive face of a width B timesthe pitch. The information strip 2 is to be readable with a high levelof reliability without involving high demands on alignment in thereading region 12. That advantage is achieved by the width B of thephotosensitive face of the photodetectors 28 being greater than 0.1 mmand by the imaging 38 in the ordinate direction Y being additionallyblurred in respect of width B by means of the one-dimensional diffuser23 (FIG. 1b) in order to tolerate a displacement perpendicularly to theplane of symmetry 13 (FIG. 1b). In addition the fineness of thesubdivision along the abscissa axis X determines the resolutioncapability of the detector arrangement 4 on the abscissa axis X. So thatthe detector arrangement 4 correctly detects the subdivision of theinformation strip 2, even if the subdivision into the N grid pairs andthe division of the M photodetectors 28 are not oriented precisely alongthe abscissa axis X and/or are not commensurable, the subdivision of thedetector arrangement 4 on the abscissa axis X must be so fine that theimage 40 of each of the N grid pairs covers at least threephotodetectors 28. For the information strip 2 with N grid pairs thenumber M of the photodetectors 28 is at least three times N. The lengthof the detector arrangement 4 is advantageously greater than the lengthof the information strip 2 to be read so that the information strip 2does not have to be precisely aligned lengthwise in the reading region12 for the reading-off operation. Accordingly the first and lastphotodetectors 28 lie outside the image 40 and only receive scatterlight. That makes it possible to measure the length of the informationstrip 2.

Instead of a single-line detector arrangement 4 it is advantageouslypossible to use a multi-line detector arrangement, for example withphotosensitive faces of the photodetectors 28 each measuring 14 μm×14 μmin 128 lines. This somewhat expensive structure permits a greater degreeof tolerance in relation to inclined orientation of the informationstrip in the reading region 12 as it is possible to compensate for therotation with respect to the plane of symmetry 13 (FIG. 1) by means ofelectronic correction.

The detector arrangements 4 considered hitherto are not designed forrecognising color components in the light 17. Instead of the detectorarrangements 4 which are sensitive to black and white, it is alsopossible to use a color-sensitive detector arrangement 4, such as forexample the CCD Linear Sensor ILX 522K from SONY. Integrated colorfilters in front of the photodetectors 28 make it possible for thecolored image 40 to be detected and analysed separately in the threeprimary colors blue, green and red, with color signals of thephotodetectors 28. If the diffraction structures 38 (FIG. 2b) and 39(FIG. 2b) differ only in spatial frequency, a single polychromaticlighting device 5 is sufficient, which emits at least light ofwavelengths λ₁, λ₂ which are predetermined by the diffraction structures38 and 39 and the lighting direction α (FIG. 2b) in order to read outthe information and check it for authenticity. The reading arrangementin this embodiment has a modified reading cycle. The single readingphase is followed in the evaluation unit 24 (FIG. 1b) by filtering ofthe color signals of the colored image 40 in accordance with thepredetermined wavelengths λ₁, λ₂ and the association of the filteredcolor signals with the grid elements 14, 15 in order to form twosequences of the detector signals S(1) and S(2) respectively. Thedetector signals S(1), S(2) correspond to the detector signals S(1),S(2) of the black-white-sensitive detector arrangement 4. Thepolychromatic lighting of the reading region 12 (FIG. 1a) at thelighting direction a does not have to be continuously switched on andoff for that purpose.

FIG. 4 which is related to FIG. 3 shows the first sequence of detectorsignals S(x,1) for the first reading phase and the second sequence ofdetector signals S(x,2) for the second reading phase, which aresuccessively produced by the M photodetectors 28 (FIG. 3). In order toclearly show the association between the detector signals S(x,1) andS(x,2) with the N grid pairs in the image 40 (FIG. 3), dotted verticallines are taken to the diagrams in FIG. 4. The detector signals S(x,1)and S(x,2) are transmitted to the evaluation unit 24 (FIG. 1b), forexample serially, through the signal line 27 (FIG. 1b) after eachreading phase, after the evaluation unit 24 has sent the reading signalthrough the signal line 27 (FIG. 1b) to the detector arrangement 4 (FIG.1b) and stored it in digitised form in the memory 29 (FIG. 1b) or 30(FIG. 1b). In addition, the second reading phase also involvesevaluation of the stored detector signals S(x,1), S(x,2). The readingcycle then begins afresh. A schematic description outlines theevaluation operation.

A computer 41 (FIG. 1b) of the evaluation unit 24 (FIG. 1b) firstlyprepares the sequences S(x,1), and S(x,2) for information recognition.For that purpose the sequences S(x,1) and S(x,2) are typically filteredand any location-dependent amplitudes and/or offsets corrected. If thesignals obtained in that way are within established ranges of signallevels ‘1’ or ‘0’, then the corresponding bit state ‘1’ or ‘0’ isassociated for x=1 through M with all detector signals S(x,1) and S(x,2)and stored as a bit signal S(x,1) and S(x,2). If one or more of thedetector signals S(x,1) and S(x,2) are disposed locally between the twolevels, the computer 41 interprets that as a consequence of partiallydestroyed grid elements 14, 15 and associates with those signals afurther state ‘undefined’. The drawing in FIG. 4 shows the regions forthe signal levels ‘0’ and ‘1’ as hatched bands.

In the view shown in FIG. 3, present in the image 40 in the second lineZ₂ at the fifth grid element 15 from the left as an example is a ‘blindspot’ 42 which has occurred as a consequence of damage to theinformation strip 2 (FIG. 1a) and which reduces the level of lightintensity of that grid element 15 in the image 40 in the second readingphase. The detector signal S(m,2) is therefore too low and the computer41 (FIG. 1b) therefore associates the state ‘undefined’ with the bitsignal S(m,2). Further ‘undefined’ states can occur in the region of theboundaries between various values of the light intensity in the image 40as the subdivision into the N grid elements 14, 15 generally does notcoincide with the division of the M photodetectors 28, for example atthe signal S(3,1) of the third photodetector 28. The fact that theimages 38 in the two reading phases, in relation to the detectorarrangement 4, are not displaced relative to each other, is a furtheradvantage of the reading arrangement, because the bit signals S(x,1) andS(x,2) are associated for each x with the common grid pair k and a pairsequence P(x) of x pairs P(x) can be formed from the sequences of thebit signals S(x,1) and S(x,2). In the ideal case there is in the pairsequence P(x) only four value combinations of the bit signals S(x,1) andS(x,2): the value combination with S(x,1)=1 and S(x,2)=0 (=‘1,0’), thevalue combination with S(x,1)=0 and S(x,2)=1 (=‘0,1’) and the valuecombinations S(x,1)=S(x,2)=1 (=‘1,1’) and S(x,1)=S(x,2)=0 (=‘0,0’). Justone pair P(x) with the value combination ‘1,1’ indicates an incompletelywritten information strip 2 and causes the computer 41 (FIG. 1b) forexample to break off the evaluation operation and/or to display a faulton the monitor 32 (FIG. 1b). The value combination ‘0,0’ may regularlyoccur exclusively at both ends of the pair sequence P(x) as thedetector, arrangement 4 projects beyond the information strip 2. Theyform two groups of i and j successive terminal pairs. In the example ofFIG. 4 these are the signals S with x=1,2 and x=M−3, M−2, M−1, M.Between the two groups of the terminal pairs the information iscontained in the M−(i+j) elements of the pair sequence P(x) which aredistributed uniformly to the predetermined number N, for example N=176,N=160 etc of the grid pairs of the information strip 2 and determine theN elements of a bit sequence B(k), the information, wherein k rangesthrough the values of between 1 and N. The value combinations ‘1,0’ and‘0,1’ respectively of the pairs of the pair sequence P(x), which areassociated with the same element B(k), determine the content of theelement B(k), if for example for an element B(k) the plurality of theassociated P(x) has the value combination ‘1,0’, B(k)=‘1’, while for thevalue combination ‘0,1’ B(k) is set=‘0’. The view in FIG. 4 shows thebit sequence B(k) obtained from the sequences S(x,1) and S(x,2), whereinhatching stands for the value ‘1’ and clear rectangles stand for thevalue ‘0’. The read-out information therefore begins with ‘10010 . . ..’

The pairs in the pair sequence P(x) with two undefined states aredisposed at the transitions from high to low or from low to highintensity values in the image 40 because the boundary between two gridpairs divides the photosensitive face of the photodetector 28 or thegrid pairs are not perfectly imaged and therefore a proportion of theimage 40 of high intensity is recorded in both reading phases by thephotodetector 28. Environmental influences such as scratches, foulingand so forth can damage the information strip 2 in such a way that therepresented information can no longer be recognised without a gap. Thedescribed encoding of the optically machine-readable information by twostates out of four possible ones affords the advantage that the damagedoes not cause the value of the grid pair to change to the other definedstate, that is to say from ‘0’ to ‘1’ or from ‘1’ to ‘0’, but to one ofthe other two undefined states.

The pairs P(x) with an undefined state and the pairs P(x) which areclearly not classified as terminal pairs, with the value combination‘0,0’, can be reconstructed on the basis of their known local positionand in comparison with their adjacent values, that is to say, attributedto those pairs P(x) are the most probable value combination ‘1,0’ and‘0,1’ respectively, the computer 41 using one of the error functionsknown to the man skilled in the art. The information is advantageouslycontained on the information strip 2 a plurality of times, for exampleas a palindrome, as even in the event of massive damage the informationcan be reconstructed from the fragments which have still been retained.

FIG. 5 shows the document 1 by way of example in the form of a personalidentity card, credit card or value card. The document 1 carries theinformation strip 2 on its surface 11 and on the surface 11 hasinformation panels 43, 44 with items of information in machine-readableplain text, such as for example name, date of birth, period of validity,nationality, biometrical data, pass number and so forth. In the case ofvalue cards, further electronic data relating to the identity of thecard are stored in an IC-module 45 and/or magnetically on a magneticstrip 46, with the latter generally being disposed on the rear of thedocument 1.

Reading units or verifying devices which are shown in FIG. 7 of as yetunpublished application CH 2557/98 and which belong to a security systemas described in CH 2557/98 are suitable for machine checking of thedocuments for authenticity by means of checking members. Instead of theoptical reader of the reading unit, described in CH 2557/98, it ispossible to use the reading arrangement described here. The text ofapplication CH 2557/98 and FIGS. 1 through 3 and 7 of CH 2557/98 areexpressly incorporated into this description. Besides the readingarrangement the reading unit includes at least one plain text reader forreading visually readable information. In addition to or also instead ofthe plain text reader a device for reading information out of theIC-module 45 and/or out of a magnetic strip 46 can be arranged in thereading unit.

What is claimed is:
 1. A reading arrangement comprising at least onedetector arrangement arranged over a strip-shaped reading region in areading plane and behind an optical imaging element, at least onelighting device arranged above the reading plane for completelyilluminating the reading region from at least a first lighting directionand an evaluation unit for machine reading of a strip-shaped informationstrip with information optically encoded as a bit sequence which isdisposed in the reading region of the reading plane, wherein a plane ofsymmetry is oriented parallel to an optical axis of the imaging elementand intersects the imaging element, the detector arrangement comprisingan at least one-line linear arrangement of photodetectors and thereading region centrally in the longitudinal direction, wherein theoptical imaging element serves to produce an image of the entire readingregion on photosensitive faces, which are oriented parallel to thereading plane, of photodetectors of the detector arrangement, theevaluation unit has a reading cycle with at least two reading phases, inthe reading phases, the lighting in the reading region differs in thelighting direction and/or the quality of the light emitted by thelighting device, the evaluation unit is adapted at least to receive andevaluate first detector signals of the photodetectors in the firstreading phase and to receive and evaluate second detector signals of thephotodetectors in the second reading phase in order to form a first andsecond sequence from the first detector signals and the second detectorsignals and, by inversion of the second sequence and comparing it withthe first sequence the read-out information is checked for correctreading-off and authenticity, to obtain a verified bit sequence, and theevaluation unit is adapted to detect an element of the first and secondsequence, respectively, out of the detector signals of at least threephotodetectors arranged in a line in mutually juxtaposed relationship.2. A reading arrangement as set forth in claim 1, wherein there areprovided at least a first and a second lighting device for lighting ofthe reading region and the emitted light of the lighting devices issubstantially monochromatic and differs in wavelengths.
 3. A readingarrangement as set forth in claim 2, wherein at least one lightingdevice comprises a linear arrangement of a plurality of light emittingdiodes.
 4. A reading arrangement as set forth in claim 1, wherein twolighting devices are provided and arranged symmetrically with respect tothe plane of symmetry.
 5. A reading arrangement as set forth in claim 1,wherein the detector arrangement is a charge coupled device.
 6. Areading arrangement as set forth in claim 1, wherein a polarizationfilter is arranged as an analyzer between the optical imaging elementand the detector arrangement.
 7. A reading arrangement as set forth inclaim 1, wherein the single lighting device comprises a lineararrangement of a plurality of light emitting diodes differing by virtueof the color of the emitted light, the light emitting diodes of thevarious colors are uniformly distributed in the linear arrangement andall light emitting diodes of the same color can be switched onsimultaneously for light emission independently of the light emittingdiodes of the other colors.
 8. A reading unit for reading a documentwith an information strip comprising a reader arrangement as set forthin claim 1, and a plain text reader included for reading visuallyreadable information of the document and/or a device for readingelectronic data out of an IC-module of the document and/or a device forreading electronic data out of a magnetic strip of the document.
 9. Areading arrangement comprising at least one detector arrangementarranged over a strip-shaped reading region in a reading plane andbehind an optical imaging element, at least one lighting device arrangedabove the reading plane for complete illumination of the reading regionfrom at least a first lighting direction, and an evaluation unit formachine reading of a strip-shaped information strip with informationoptically encoded as a bit sequence which is disposed in a readingregion of the reading plane, wherein a plane of symmetry is orientedparallel to an optical axis of the imaging element and intersects theimaging element, the detector arrangement comprising a linear and atleast single-line arrangement of photodetectors and the reading regioncentrally in the longitudinal direction, wherein arranged over thereading plane is at least one polychromatic lighting device for completeillumination of the reading region from the lighting direction by meansof lighting beams which contain light of at least two predeterminedwavelengths, the optical imaging element serves to produce a coloredimage of the entire reading region on photosensitive faces, which areoriented parallel to the reading plane, of photodetectors of thedetector arrangement, the photodetectors have color filters in front ofthe photosensitive face to allow the detection and analysis of thecolored image in the three primary colors blue preen and red, and toproduce color signals of each primary color, the evaluation unit has areading cycle with a first phase for registering the color signals fromthe photodetectors, followed by a second phase for filtering the colorsignals in accordance with the predetermined wavelengths and anevaluation phase for producing first and second detector signalsequences, and the evaluation unit is adapted at least to receive andevaluate the three color signals of the photodetectors in accordancewith the predetermined wavelengths and to form a first sequence of thefirst detector signals for the first predetermined wavelength and asecond sequence of the second detector signals for the secondpredetermined wavelength and by inversion of the second sequence andcomparing with the first sequence the read-out information is checkedfor correct reading-off and authenticity in order to form a verified bitsequence, from the two sequences.
 10. A reading arrangement as set forthin claim 9, wherein the detector arrangement is a charge coupled device.11. A reading arrangement as set forth in claim 9, wherein apolarization filter is arranged as an analyzer between the opticalimaging element and the detector arrangement.
 12. A reading arrangementas set forth in claim 9, wherein the single lighting device comprises alinear arrangement of a plurality of light emitting diodes differing byvirtue of the color of the emitted light and the light emitting diodesof the various colors are uniformly distributed in the lineararrangement and emit light simultaneously to provide the polychromaticlight.
 13. A reading unit for reading a document with an informationstrip comprising a reader arrangement as set forth in claim 9, and aplain text reader included for reading visually readable information ofthe document and/or a device for reading electronic data out of anIC-module of the document and/or a device for reading electronic dataout of a magnetic strip of the document.
 14. A reading arrangementcomprising at least one detector arrangement arranged over astrip-shaped reading region in a reading plane end behind an opticalimaging element, at least one lighting device arranged above the readingplane for completely illuminating the reading region from at least afirst and second lighting direction and an evaluation unit for machinereading of said strip-shaped information strip with informationoptically encoded as a bit sequence which is disposed in the readingregion of the reading plane, wherein a plane of symmetry is orientedparallel to an optical axis of the imaging element and intersects theimagine element, the detector arrangement comprising an at leastone-line linear arrangement of photodetectors and the reading regioncentrally in the longitudinal direction, wherein the optical imagingelement serves to produce an image of the entire reading region onphotosensitive faces, which are oriented parallel to the reading plane,of photodetectors of the detector arrangement, there are provided atleast a first and a second lighting device for lighting of the readingregion, the emitted light of the lighting devices is substantiallymonochromatic and of the same color, the evaluation unit has a readingcycle with at least two reading phases, each reading phase differs fromthe preceding one by the direction of the light emitted by one of thelighting devices, the evaluation unit is adapted at least to receive andevaluate first detector signals of the photodetectors in the firstreading phase and to receive and evaluate second detector signals of thephotodetectors in the second reading phase in order to form a first andsecond sequence from the first detector signals and the second detectorsignals and by inversion of the second sequence and comparing with thefirst sequence the read-out information is checked for correctreading-off and authenticity, and wherein the evaluation unit is adaptedto detect an element of the bit sequence out of the detector signals ofat least three photodetectors arranged in a line in mutually juxtaposedrelationship.
 15. A reading arrangement as set forth in claim 14,wherein at least one of the lighting devices comprises a lineararrangement of a plurality of light emitting diodes and that the lightemitting diodes emit light in at least the first and second lightingdirection respectively.
 16. A reading arrangement as set forth in claim14, wherein two lighting devices are provided and arranged symmetricallywith respect to the plane of symmetry.
 17. A reading arrangement as setforth in claim 14, wherein the detector arrangement is a charge coupleddevice.
 18. A reading arrangement as set forth in claim 14, wherein apolarization filter is arranged as an analyzer between the opticalimaging element and the detector arrangement.
 19. A reading unit forreading a document with an information strip comprising a readerarrangement as set forth in claim 14, and a plain text reader includedfor reading visually readable information of the document and/or adevice for reading electronic data out of an IC-module of the documentand/or a device for reading electronic data out of a magnetic strip ofthe document.